It is known how to ensure protection of an electric installation against voltage surges by means of devices including at least one component for protection against voltage surges, in particular one or several varistors and/or one or several spark-gaps. Such devices are currently designated by the term of lightning arrester. For single-phase installations, a varistor can be connected between the phase and the neutral while a spark-gap is connected between the neutral and the ground. For three-phase installations, varistors can be between the different phases and/or between each phase and the neutral and a spark-gap between the neutral and the ground. For electric installations operating with a DC current, for example for installations of photovoltaic generators, resort is also made to varistors and optionally spark-gaps.
The use of a spark-gap as a protective device against voltage surges may pose a problem for dealing with the follow current of the spark-gap. Indeed, because of priming of the spark-gap, a current may continue to flow through the primed spark-gap and this even after the end of the transient voltage surge. This current is sustained by the voltage source of the electric installation to be protected. This current then corresponds to a follow current which is desirably cut off by breaking the arc formed in the spark-gap. This problem of cutting off the follow current is notably posed in the case of an electric installation operating under a DC current such as an installation for photovoltaic generation of electricity.
Exemplary embodiments of the present disclosure are related to lightning arresters for which different breaker systems can be used.
For example, in the case when an arc only forms between two electrodes at the end of the life of the varistors, there exist single-use breaker systems including mechanical short-circuiting of the arc and then dealing with the short-circuit current with a fuse.
In another example, a spark-gap can be used as a lightning arrester, arcs are repeatedly formed between the electrodes of the spark-gap, preventing the use of single-use breaker systems which are unsuitable. The cutting-off of arcs which repeatedly form, moreover corresponds to a need for other pieces of equipment for which the purpose is to cut off a current as a result of a fault, or any external action. Multiple-use breaker systems can be used both for pieces of equipment such as contactors, circuit breakers or switches and for lightning arresters with spark-gaps.
The systems disclosed herein are based on enlarging the distance between the electrodes between which the arc forms or on separating the arc into a multiplicity of arcs. In both cases, the cutting-off of the arc is achieved by raising the so-called arc voltage to a sufficiently high value so that the voltage source is no longer capable of maintaining this arc voltage. Thus, when the voltage of the source is high, the multiple-use breaker systems should allow an all the greater enlargement of the distance between the electrodes or an all the greater separation into a multiplicity of arcs. For high operating voltages which may be encountered in photovoltaic installations, for example between 500 and 1,000V or even up to 1,500V because of the DC nature of the current, adaptation of the previous systems to the cutting-off of such voltage levels may lead to significant dimensional constraints. Now lightning arrester devices can be contained in casings said to be “mountable” on a DIN rail. These casings do not exceed a width of 17.5 mm and a length of 92 mm, and are then too small for being able to meet such dimensional constraints.
Therefore there exists a need for a method for cutting off an electric arc with which the bulkiness of the devices applying it, may be less significant.
Exemplary embodiments of the present disclosure are directed to a method for cutting off an electric arc which forms between two main electrodes, the method including displacing the electric arc formed towards an electrode located in an intermediate position between both main electrodes, separating the electric arc formed into two secondary electric arcs between the main electrodes and the intermediate electrode, a semiconductor switch normally open, connecting the intermediate electrode to one of the main electrodes, closing the semiconductor switch for extinguishing the secondary electric arc between both electrodes which are connected by the semiconductor switch, opening the semiconductor switch in order to extinguish the other secondary electric arc.
In an exemplary embodiment disclosed herein, the method includes a time-out after separation of the arc formed into two second electric arcs in order to prevent an arc from being re-formed between both main electrodes upon closing the semiconductor switch.
In another exemplary embodiment, the method includes a time-out after closing the semiconductor switch in order to prevent the extinguished arc from being re-formed between the intermediate electrode and one of the main electrodes upon opening the semiconductor switch.
In another exemplary embodiment, a method for protecting an electric installation against transient voltage surges is disclosed, the method applying the cutting-off of an electric arc according to the previous cut-off method when a transient voltage surge occurs in the electric installation to be protected causing the formation of a first electric arc between both main electrodes, the main electrodes being connected to the electric installation to be protected.
According to the present disclosure, an exemplary electric installation is connected to a low voltage electricity distribution network.
According to another exemplary embodiment, an electric installation operates under a DC current, such as an installation for photovoltaic generation of electricity.
An exemplary embodiment of the present disclosure is directed to a protection device for protecting an electric installation against transient voltage surges, including two terminals for connecting the device to the electric installation to be protected, a first main electrode and a second main electrode, each main electrode being connected to respectively one of the connection terminals, an electrode located in an intermediate position between the first main electrode and the second main electrode, a semiconductor switch, normally open, connecting the intermediate electrode to the first main electrode, a circuit for controlling the semiconductor switch, the control circuit being provided in order to successively ensure closing of the switch, and then opening of the switch, after an electric arc formed between the main electrodes has been divided into two arcs via the intermediate electrode.
According to an exemplary embodiment, the semiconductor switch is an insulated gate bipolar transistor or a field effect transistor with a metal-oxide gate.
According to another exemplary embodiment, the control circuit ensures a time-out between the division of the electric arc into two arcs via the intermediate electrode and the closing of the switch and/or between the closing of the switch and the opening of the switch.
According to another exemplary embodiment, the electrodes are fixed, both main electrodes being positioned facing each other from a first side to a second side and forming a spark-gap; and the intermediate electrode partly extending between both main electrodes from the second side.
According to an exemplary embodiment, the device includes a unit for triggering an arc between the main electrodes if a transient voltage surge occurs on the electric installation to be protected, the triggering unit including an electrode for triggering an arc from the first side of the main electrodes.
According to an exemplary embodiment, the intermediate electrode has a wedge-shaped end portion on the side where the intermediate electrode extends between both main electrodes.
According to the present disclosure, the exemplary protection device includes a magnet positioned in order to displace, in the direction from the first side to the second side, an electric arc which forms between the main electrodes of the spark-gap and/or the main electrodes being divergent from the first side to the second side.
According to an exemplary embodiment, the device includes an additional connection terminal and an additional spark-gap formed by two additional electrodes, one of the additional electrodes being connected to the additional terminal and the other one of the additional electrodes being connected to one of the two terminals for connecting the device to the electric installation.
According to an alternative, the device is specially designed for applying the previous method.